Two types of ammunition are generally recognized; traditional supersonic ammunition, which fire projectiles with velocities exceeding the speed of sound (which depends on the altitude and atmospheric conditions but is generally in the range of 1,000-1,100 feet per second (fps), most commonly given at 1,086 fps at standard atmospheric conditions), and subsonic ammunition which fire projectiles with velocities less than that of the speed of sound. The lower speed of subsonic ammunition makes it much quieter than typical supersonic ammunition. Ideally, these subsonic rounds need to work interchangeably with supersonic rounds, i.e., fit properly in the same firearm chamber.